1. Field of the Invention
The present invention relates to an imaging apparatus provided with an imaging device having sensitivity in visible and infrared regions.
2. Description of the Related Art
In general, imaging devices such as charge coupled devices (CCDs) and complementally metal oxide semiconductor sensors (CMOS sensors) exhibit sensitivity not only to visible light but also to infrared light. When an image is taken using such imaging devices in a dark environment, a high-sensitivity monochrome image can be obtained by utilizing the infrared light component to obtain a luminance component. On the other hand, in order to obtain a color image having good color reproducibility, the infrared light component must be removed.
In Japanese Patent Laid-Open Publication No. Hei 6-105319, a method using an imaging device and an infrared light receiving device is disclosed in which the output signal of the infrared light receiving device (i.e., an infrared component) is subtracted from the output signal of the imaging device (i.e., the sum of a visible light component and the infrared light component).
In order to obtain a color image having good color reproducibility using the imaging device described above, the infrared light component must be removed. Furthermore, when an image is taken in a dark environment, it is desirable to achieve a high-sensitivity monochrome image by incorporating the infrared light component to obtain a luminance component.
In Japanese Patent Laid-Open Publication No. Hei 6-105319, a method using an imaging device and an infrared light receiving device is disclosed in which a luminous component is extracted from an output signal containing an infrared light component. Specifically, the output signal of the infrared light receiving device (i.e., the infrared light component) is subtracted from the output signal of the imaging device (i.e., the sum of visible light and infrared light components). When the subtraction result is less than a certain threshold value, the output signal from the solid imaging device is subjected to color suppression rather than subtraction processing, and as such the luminous component is extracted from the output signal containing the infrared light component. In this manner, a color image having good color reproducibility can be obtained when the image is taken in a bright environment, and a high-sensitivity monochrome image can be taken in a dark environment.
However, in the method disclosed in Japanese Patent Laid-Open Publication No. Hei 6-105319, when the spectral characteristics of a visible light filter provided in the imaging device and of an infrared light filter provided in the infrared light receiving device are different in the infrared region, the infrared light component cannot be satisfactorily removed from the output signal of the imaging device. Hence, a problem exists in that good color reproducibility cannot be obtained.
Furthermore, in the method disclosed in Japanese Patent Laid-Open Publication No. Hei 6-105319, switching between a color image and a monochrome image is done instantaneously. Hence, a problem exists in that the person taking the image has an uncomfortable feeling.